1. Field of the Invention
The present invention relates to a receiving terminal of a mobile communication system, and more particularly, to a triple band receiving terminal of a mobile communication system. The terminal can be used in three bands by adding a circuit to a dual band mobile communication terminal.
2. Background of the Invention
Recently, a popular mobile communication terminal needs to have, multi-function, diversification and compatibility improvement, the terminal also has to be compatible with equipments related to the Internet. The mobile communication terminal market has been rapidly expanded. In addition, interests in a dual band mobile communication terminal usable as a two-way system of a GSM (global system for mobile communication) and a DCS (digital cellular system) in Europe have increased. A triple band mobile communication terminal usable in a PCS (personal communication system) besides the GSM and the DCS and usable all over the world is even more in demand.
The GSM is a TDMA (time division multiple access) digital system commonly used in European countries. The GSM supports non-synchronous and synchronous data communication, it can be linked with an ISDN, a packet switching network, the Internet, as well as a voice communication. The GSM is operated in a 900 MHz frequency band.
The DCS (digital cellular system) having a frequency range of 1800 MHz for a European PCN (personal mobile communication network) is a system upbanding the GSM. A CDMA (code division multi access) type PCS (personal communication system) uses a signal having 1900 MHz band and provides various kinds of radio communication services such as voice, data and fax, etc.
FIG. 1 is a circuit diagram illustrating a dual band receiving apparatus of a mobile communication terminal of a related art. As depicted in FIG. 1, the dual band receiving apparatus allows the mobile communication terminal operate in two bands, a 900 MHz EGSM (extended global system for mobile communication) and a 1800 MHz DCS (digital cellular system).
The dual band receiving apparatus includes a filter unit 10 receiving a signal inputted through an antenna and passing a pertinent frequency, an amplifier unit 20 amplifying the signal passing through the filter unit 10, a phase shift unit 40 receiving an oscillation frequency outputted from a local oscillator 30 and phase-modulating the frequency, and a mixing unit 50 mixing the oscillation frequency outputted through the phase shift unit 40 with the signal received through the amplifier unit 20 and outputting an intermediate frequency signal. That is, the dual band receiving apparatus of the mobile communication terminal includes a filter, a low noise amplifier, a mixer and a phase shift in order to receive signals in different bands. In addition, the amplifier unit 20, the mixing unit 50, the phase shift unit 40 and the local oscillator 30 construct a RF (radio frequency) receiver (R1) for dual band.
However, according to regional characteristics or user's preferences, a mobile communication terminal has to be used as a PCS (personal communication system) or a DCS (digital cellular system) or a GSM (global system for mobile communication). Because the mobile communication has to satisfy all three bands, a triple band receiving terminal is required.
FIG. 2 illustrates a triple band receiving apparatus of a mobile communication terminal of a related art. As depicted in FIG. 2, the triple band receiving apparatus allows the mobile communication terminal operate in multiple bands, a 900 MHz EGSM (extended global system for mobile communication), a 1800 MHz DCS (digital cellular system) and a 1900 MHz PCS (personal communication system).
The triple band receiving apparatus of the mobile communication terminal includes a first filter 11, a second filter 12 and a third filter 13 passing only a reception frequency corresponding to each frequency band among signals received through an antenna. A third LNA (low noise amplifier) 23 amplifies a signal outputted from the third filter 13, a fourth filter 14 eliminates the image signal outputted from the third LNA 23 and a RF (radio frequency) receiver (R2) mixes the signals passing the first 11, the second 12 and the fourth filters 14 with the oscillation frequency and outputs an intermediate frequency.
The RF receiver (R2) includes a first 21 and a second LNA (low noise amplifier) 22 amplifying signals passing the first 11 and the second filters 12, a first 41, a second 42 and a third 43 phase shifters receiving the oscillation frequency outputted from the local oscillator 31. Then, the RF receiver (R2) modulates the signals in quadrature, a first 51, a second 52, a third 53, a fourth 54, a fifth 55 and a sixth 56 mixers mix the oscillation frequency outputted from the first 41, the second 42 and the third phase 43 shifters with the signal outputted from the first 21 and the second LNA 22 and the fourth filter 14, then, outputs an intermediate signal.
The first filter 11 passes a 900 MHz band signal, the second filter 12 passes a 1800 MHz band signal, and the third filter 13 passes a 1900 MHz band signal. Further, the fourth filter 14 eliminates an image signal existed in the signal outputted from the third LNA 23, then divides the image signal into positive and negative portions and subsequently inputs them to the fifth 55 and the sixth 56 mixers respectively in order to eliminate more noise elements.
In order to use the conventional dual band mobile communication terminal in three bands, the RF receiver has to be replaced into a triple band RF receiver. In this triple band RF receiver, each terminal corresponds to each frequency band, and a low noise amplifier and a filter for a PCS have to be additionally implemented, therefore, production process and production cost are increased.
In addition, in the conventional triple band receiving apparatus for the mobile communication terminal, implementing a RF receiver includes each terminal for each frequency band. Because an internal circuit construction is complicated and its volume is increased, it runs contrary to the recent mobile communication system trend of miniaturization and light-weight.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.